Sperm sexing: How does it affect bovine sperm-oviduct interactions?

Sperm sexing allows for the control of sex in future offspring, which is particularly useful in the bovine dairy industry where females are in high demand. However, the widespread use of sexed sperm is hindered primarily by reduced fertility, which can be lowered by as much as 25% after sperm sexing. The reasons for this phenomenon are currently unknown. This study therefore aims to characterise sperm-oviduct interactions after sexing through the use of live cell imaging, scanning electron microscopy, confocallaser scanning microscopy and fluorescence microscopy. Scanning electron microscopy showed that the number of bound sperm in the sperm reservoir is decreased in sexed sperm as compared to conventional sperm of the same individual. Further to that, sexed sperm reveal deformations in the head as well as sharp bends in the neck and the mid piece of the tail. Increased amounts of debris are also seen on the sperm plasma membrane. Moreover, the ciliated cells of the oviduct do not embrace the head of the sexed sperm as they do in conventional sperm, suggesting there is a lack of recognition of the sexed sperm by the oviduct. Fluorescent localisation of calcium revealed that there is a trend for the number of sperm with calcium in both the acrosome and post-acrosomal regions of the sperm head to decrease after sexing. Our results imply that sperm sexing compromises the formation of the sperm reservoir by altering sperm binding to the tubal epithelium. Further to that, sperm motility is negatively affected through deformations in the tail. This results in reduced numbers of sperm reaching the oocyte and being able to fertilize.